1. Field of the Invention
The present invention relates to an image forming apparatus for forming an image of image information, in accordance with light having the image information such as light reflected from a document, and more particularly to an image forming apparatus utilizing a light image memory for storing the image information temporarily.
2. Description of the Related Art
Recently, an image forming apparatus such as an electrophotographic copying machine has been implemented with various kinds of functions such as multiple copying, both side copying, composite copying etc.
Generally, the conventional copying machine has a document scan type optical system comprising a scanner movable along a document set on a document table, wherein light reflected from the document is projected onto a photoconductive drum through mirrors and lenses. Therefore, in the optical system, it is necessary to scan the whole area of the document once in order to produce a copy of the document. In order to produce plural copies of the document, it is necessary to scan the document a number of times repeatedly corresponding to the number of copies, resulting in that it takes a long time to produce those plural copies. In this case, each time the document is scanned, a return time required for the scanner to return from the end position of the scanner in the scan operation to an original position thereof tends to take a longer time.
Furthermore, after plural copies of a set of documents are produced, the produced plural copies are discharged every set of documents in the order of the documents by using either of the following apparatuses:
(1) a sorter for discharging each set of copied papers corresponding to each set of documents, to each of plural trays, respectively.
(2) a document circulation type automatic feeding apparatus for producing plural copies of documents by circulating the documents a number of times corresponding to the number of copies.
However, such a problem is caused that the copying machine comprising the sorter becomes large, and also, in the copying machine comprising the above automatic feeding apparatus such a problem is caused that the document is damaged easily.
In order to solve the above problems, there has been proposed an automatic document processing apparatus in the Japanese Laid-open Patent Publication (JP-A) No. 140542/1979. There has also been proposed a method for projecting reflected light of an image written in a light image memory which is arranged on each surface of a regular polyhedron member so as to form an electrostatic latent image on a photoconductive body in the Japanese Laid-open Utility Model Publication (JP-A) No. 139852/1979. In former apparatus, an image of a document is temporarily written in a light image memory including liquid crystal, an electrochromic material, PLZT (compound of Pb, La, Zr and Ti), and thereafter, the image of the document is read out from the light image memory, and it is recorded onto a recording body, or an electrostatic latent image corresponding to the image of the document is formed onto a photoconductive body.
However, when image information is written in the aforementioned light image memory and is read out therefrom many times repeatedly, the performance of writing image information and the performance of storing image information deteriorate, resulting in that the image information may not be stored therein properly.
Furthermore, since the aforementioned light image memory can store image information for a certain time, the same image can be repeatedly formed thereon to make plural copies. However, on the contrary, there is a possibility of leaking image information of a secret document.
Furthermore, foreign matter such as dust may adhere to the aforementioned light image memory, and then, the image of the dust is formed as an image defect with the image of the document to be formed. Particularly, in the case that the aforementioned light image memory is mounted detachably to the main body of the copying machine so as to exchange it for another light image memory having photosensitivity characteristics, dust may adhere to the detached light image memory and also the surface thereof may be marred, resulting in that they are formed as an image defect thereon.
In the aforementioned copying machine, the reflected light from the document is projected onto the photoconductive body so as to form an electrostatic latent image thereon. For example, in the case of a photoconductive body having a photoconductive layer, after the surface of the photoconductive body has been uniformly electrified, the reflected light from the document is projected on to the photoconductive layer. Then, the resistance of the photoconductive layer onto which the reflected light is projected decreases, and part of the charge on the surface thereof is canceled so as to form an electrostatic latent image on the photoconductive body. Thereafter, generally, toner is applied to a portion where the charge has not been canceled, i.e., the reflected light has not been projected, to render the latent image to be developed into a visible toner image.
However, in the case that the image is formed by using the aforementioned light image memory, toner may adhere to the circumference of the image forming portion. This is caused because of the following reason. Since light is not projected onto the circumference of the image forming portion, the charge on the surface thereof is not canceled, resulting in that excessive toner may adhere to the circumference of the portion (the image forming portion) corresponding to the light image memory. If a sheet of paper onto which the toner image is transferred has approximately the same size as that of the light image memory, the excessive toner remains on the photoconductive body, and then, the excessive toner is abandoned. On the other hand, if the size of the paper is larger than that of the light image memory, the excessive toner is transferred onto the paper, and then, the excessive toner image having a frame shape is formed in the circumference of the image forming portion. Furthermore, when the excessive toner is used for each image formation, such a problem is caused that the cost required for forming the image increases.